Studies on serial patient isolates of HIV-1 have correlated different patterns of cytotropism and virulence with the sero-positive pre-AIDS and AIDS phases of disease. Relatively few studies have been undertaken on the characterization of serial isolates with respect to host antibody responses. Here we have studied the evolution of HIV-1 envelope glycoproteins with respect to neutralizing responses. (1) Molecular clones of serial patient isolates representing the progression from the healthy sero-positive to the AIDS phase of infection have been tested for relative susceptibility to neutralization by a panel of antibodies. (2) The same molecular clones have been evaluated for their ability to raise neutralizing antibody. These latter tests have used a novel method of immunization $ direct inoculations of Env-expressing plasmid DNA (in vivo transfection). DNA vaccines have also been used in macaques to test the ability of this novel form of immunization to raise pr otective immunity. Envs that display changes in susceptibility to neutralization, or ability to raise neutralizing antibody, will be mapped for the mutations that caused these changes. The growth characteristics and syncytium-inducing capacities of the serial Envs will also be characterized. This will allow evaluation of how mutations that affect susceptibility to neutralization or immunogenic potential affect growth characteristics. Laboratory strains with different neutralization and growth characteristics will be evaluated for susceptibility to neutralizing antibody and immunogenic potential to test how results with these viruses compare to those with the serial patient isolates. These studies should contribute to the development of vaccines that can protect against viruses representing different phases of infections. They may also provide information on the role of neutralizing antibody and immunogenic potential in the selection of viruses with different growth characteristic s.